1. Field of the Invention
The invention relates to interference cancellation in a receiver operating in a radio system.
2. Description of the Related Art
With increasing numbers of mobile communication systems and their users, there is a growing demand for placing the systems on overlapping or at least nearby frequencies. In other words, guard bands between the systems must be narrowed. This inevitably leads to a potential increase of interference between the radio systems, which will have to be taken into account in system design.
One way of cancelling interference in radio systems implemented using spread spectrum technology is the IRC method (Interference Rejection Combining), in which receiving antennas are suitably weighted in an attempt to obtain an optimal result regarding the quality of the signal to be detected. However, the weighting of antennas does not provide a satisfying solution in a situation in which signal detection is interfered by a signal originating from another radio system. The situation can be illustrated with FIG. 1, where two radio systems operate within the same geographical area. A base station 100 belongs to a first radio system and serves a terminal 104. A base station 102, in turn, belongs to a second radio system and serves a terminal 106. The terminal 106 located in the coverage area 110 of the base station 100 is far away from its serving base station 102 and therefore has to use high transmission power. Upon reception at the base station 100, the terminal 104 using low transmission power experiences significant interference caused by the transmission of the terminal 106 belonging to the second system.
It is therefore obvious that there is a need to develop a solution for signal reception that allows radio systems to be placed on adjacent and overlapping frequencies, without the transmissions of the neighbouring systems interfering unreasonably with each other.